1. Field of the Invention
The present invention relates generally to semiconductor device fabrication, and more particularly to semiconductor wafer processing systems.
2. Description of the Background Art
Semiconductor wafer processing systems that have more than one module are referred to as “cluster tools.” Typically, a cluster tool has a load lock module for receiving a semiconductor wafer, one or more process modules for performing fabrication steps on the wafer, and a transport module for moving the wafer from the load lock module to a process module, and vice versa. Exemplary cluster tools are disclosed in U.S. Pat. No. 4,917,556 to Stark et al. and U.S. Pat. No. 5,186,718 to Tepman et al., both of which are incorporated herein by reference in their entirety.
The arrangement of modules in a semiconductor wafer processing system (i.e., the system's architecture) directly affects throughput. Throughput is an important performance measure of a semiconductor wafer processing system because it is related to productivity: the higher the throughput, the more wafers that can be processed within a given amount of time. Accordingly, the cost of ownership of a semiconductor wafer processing system and the fabrication cost per wafer depend on throughput.